This invention relates to splitting an ATM connection into multiple sub-connections so that call blocking is reduced and a network is better utilized. Specifically, this invention relates to a system and method for splitting a network ATM connection and sending a message through these sub-connections. This invention is embodied in a network system using connection splitting and in methods for splitting an incoming ATM cell flow before being sent through sub-connections.
Contemporary networking services can be categorized into two functionally orthogonal technologies, namely, connection-less and connection-oriented protocols. In the connection-less category, Internet Protocol (IP) continues to dominate the current market. The primary advantages of IP are its low initial latency for data transfer and its potential for fine-grain network load balancing which is achieved through packet level routing.
On the other hand, connection-oriented protocols like ATM perform call level routing which offers a natural way of reserving network resources for end-applications. However, ATM has lesser control on bandwidth fragmentation which is caused by its call level routing.
Bandwidth fragmentation occurs when a connection occupies a part of a link bandwidth leaving the rest of the bandwidth unused. Such an unused bandwidth becomes fragmented when it is not enough for a new connection. Therefore, it is desirable to have an ATM network with a more balanced load and improved blocking performance, while maintaining its inherent resource reservation and Quality of Service (QoS) features.
Connection splitting according to the present invention shares some common ideas with the technique of Inverse Multiplexing, used in the Public Switched Digital networks (PSDN). Inverse Multiplexing (IM) is a mechanism for combining multiple switched digital channels to create a single high bandwidth end-to-end connection. See J. Duncanson, xe2x80x9cInverse Multiplexingxe2x80x9d, IEEE Communications Magazine, April 1994, pp. 34-41. Both for ATM splitting and IM, multiple sub-connections have to be setup before the protocol operations start. Additionally, in case of IM multiple phone numbers have to be dialed. A splitting mechanism at the source and a joining mechanism at the destination are also necessary in both the approaches. Despite these functional similarities, the implementation approaches are significantly different. In case of Inverse Multiplexing, framing bits are used for inter-channel synchronization which is an essential information for frame ordering at the destination. In addition, the standard xe2x80x9cAggregation of Multiple Independent 56 kbit/s or 64 kbits/s channels into a Synchronized Wideband Connectionxe2x80x9d, for IM also allows to put numbered frames of 256 octets, which makes cell ordering relatively more straightforward. See ANSI Draft from TIA Committee TR41.4, pp. 3014.
At least the following problems exist in conventional ATM networks:
Unused bandwidth leaves the network bandwidth fragmented
Fragmented bandwidth leads to wastage of precious network resources
It is an objective of this invention to solve the above-mentioned problems in conventional ATM networks in an efficient manner. Specifically, it is an objective of this invention to allow an ATM network to use connection splitting to reduce call blocking and provide less bandwidth fragmentation.
Since conventional ATM does not provide any mechanism for cell sequencing, it is an objective of the present invention to design a set of split and join scheduling protocols to handle out-of-order delivery of cells caused by splitting. The reasons for such out-of-order delivery include cell loss and varying cell transfer delay through different sub-connections. It is found that if cells are lost it is not possible to avoid the out-of-order delivery completely. Therefore, a specific objective of this invention is to design the split and join scheduling algorithms carefully so as to maintain the probability of cells being delivered out-of-order within an acceptable range.
Another important objective of the present invention is to keep the users, as well as the network, insulated from the effects of connection splitting. Such user transparency is required to keep the splitting scheme compatible with the existing applications. Network transparency also allows existing switching equipments to handle splitting without any hardware and software modifications. It also makes the scheme architecturally open and, therefore, allows easy deployment of traffic control mechanisms like ABR flow control over split connections.
In order to achieve the above objectives the present invention provides a technique for splitting a single ATM connection into multiple sub-connections and then to route each of the sub-connections independently. Further, the ATM cell-flow at the source is partitioned and sent through the sub-connections. Then, at the destination, all the sub-flows are joined again to reconstruct the original cell flow.
In the present invention, all the splitting related data-plane functions are encapsulated at the ATM Adaptation Layer (AAL) of the source and the destination. Also, the signaling enhancements are implemented as a separate layer which works on top of the regular ATM signaling stack. And these enhancements are required only at the end-stations.
The present invention potentially enhances capacity utilization by improving network load balancing. As a result, for a given network the present invention facilitates more user traffic and reduces call blocking experienced by high-bandwidth connections. The requirements for such a performance are that the sub-connections must comply with the required QoS of the application, and their aggregated User Parameter Control (UPC) profile should match with the original traffic parameters.
The present invention also uses a new type of ATM resource management (ATM RM) cell for cell sequencing. The ATM RM cell is an important component of this invention that makes the implementation of ATM connection splitting significantly different from the conventional Inverse Multiplexing technique.
Specifically in order to accomplish the objectives of this invention, a method of splitting an ATM connection is provided between a source and a destination into a plurality of sub-connections, wherein said messages comprise ATM data cells, said ATM data cells being transmitted using more than one of said plurality of sub-connections, said splitting being done for transmitting messages in an ATM network such that said ATM network has reduced call blocking.
Further improvements include a method wherein Resource Management (ATM RM) cells are added to a flow of the ATM data cells, wherein they are used for an ordered delivery of said ATM data cells.
Another aspect of the present invention is a method of scheduling a source in an ATM network the method comprising selecting a predetermined degree of splitting, a flow distribution, UPC specifications, a value of periodicity Nrm of ATM RM cells and a new sub-connection; setting an ATM RM sequence counter to zero; sending an ATM RM cell and increasing the ATM RM sequence counter by one; sending Nrm number of ATM data cells through the selected sub-connection; checking flow distribution specification; determining if sub-connection is to be switched; repeating the steps if sub-connection is not to be switched and selecting a new subconnection and repeating the steps if sub-connection is to be switched.
Yet another aspect of the present invention is a method of scheduling a sink in an ATM network, said method comprising selecting a predetermined degree of splitting, flow distribution, selecting UPC specifications, selecting a value of periodicity Nrm of ATM RM cells; queuing the ATM data cells for each sub-connection in a corresponding sink buffer; setting the value of a variable Expected ATM RM (ERM) to zero; scanning all the sink buffers and selecting a buffer with the smallest numbered ATM RM cell in front of it; dropping all ATM data cells until the next ATM RM cell if the ATM RM cell selected is less than the value of the variable ERM; clocking available ATM data cells in the sink buffer if the ATM RM cell selected in is not less than the value of the variable ERM; updating the value of the variable ERM to one more than the sequence number of the ATM RM cell selected; delivering the available ATM data cells; repeating for all the sink buffers.
Further improvements include the previous method wherein ATM data cells are clocked only if there are Nrm or less cells within two surviving ATM RM cells in a sink buffer, otherwise they are dropped.
Still further improvements include the previous method wherein said sink scheduling is initiated only after all sink buffers are filled with at least two ATM RM cells.
An improvement includes a method wherein Nrm is chosen based on an application""s burst tolerance. Further improvement has an Nrm of at least 32.
An improvement includes a splitting method wherein a PNNI protocol is used to setup split sub-connections for transferring messages. Still further improvements include a splitting method wherein the sub-connections are setup prior to routing using PNNI. In another improvement the sub-connections are setup after routing using PNNI.
Another aspect of this invention includes a method of transferring a message using PNNI protocol, said method comprising: splitting an arrived call into a predetermined number of sub-calls if the call requires a bandwidth higher than a predetermined threshold; making a PNNI routing decision for each of said sub-calls; making a PNNI routing decision for the original call if the message is not split; blocking the call if the calls and the sub-calls that are routed are not acceptable; accepting the call if sub-calls are acceptable.
Another aspect of this invention includes a method of transferring a message using PNNI protocol, said method comprising: making a PNNI routing decision on an arrived call; accepting the call if the call is acceptable; splitting the arrived call into a predetermined number of sub-calls if the call is not acceptable and requires a bandwidth higher than a predetermined threshold; making a PNNI routing decision for each of said sub-calls; blocking the call if the sub-calls that are routed are not acceptable; accepting the call if the sub-calls are acceptable.
Another aspect of this invention is a connection-splitting network system for transferring messages using ATM comprising a source, a sink, a source scheduler; and a sink scheduler, wherein, a connection from said source is split into multiple sub-connections by a splitter signalling module, multiple sub-connections are established between said source and said sink, said messages are segmented into ATM data cells, said ATM data cells are sent to multiple sub-connections by said source scheduler, and the sink scheduler reassembles the message at said sink.
Further improvements include a network system wherein each of said source scheduler and said sink scheduler are placed in a split sub-layer, said split sub-layer being part of a connection splitting ATM Adaptation Layer (AAL) that is placed above a conventional ATM layer, said split sub-layer comprising buffers and said connection splitting AAL comprising a native AAL layer and the split sub-layer.